Antifoggant combination for processing evaporated silver halide layers



United States Patent No Drawing. Filed Oct. 22, 1965, Ser. No. 502,390 8 Claims. (Cl. 9661) ABSTRACT OF THE DISCLOSURE Heterocyclic mercaptans and soluble silver halide complex formers are used both to prepare new binderless silver halide photographic elements which have reduced tendency to f-og during development and to produce a new developing process for binderless silver halide photographic elements, which process tends to reduce the fog normally produced upon development.

This application is a continuation-in-part of US. patent application Ser. No. 428,204, filed Jan. 26,- 1965, and US. patent application Ser. No. 361,243, filed Apr. 20, 1964.

This invention relates to the control of development fog in the processing of binderless, silver-halide photographic layers. One important aspect of our invention concerns a synergistic antifoggant combination for use in the processing of evaporated silver halide light sensitive layers. It also relates to novel photographic elements.

It is well known that photosensitive silver halide can be prepared without the usual colloidal vehicle, for example, by vapor deposition in high vacuum of one or a mixture of silver halides onto a support such as paper, plastic, film or glass. After exposure to a light im-age such layers are processed conventionally by surface application of, or immersion in, successive developing and fixing solutions. Combined developing and fixing compositions, so-called mono-baths, which contain both a developing agent and a fixing agent can also be used. However, binderless, e.g., vapor-deposited, silver-halide films tend to develop non-selectively, that is to say, show a rapid rate of fog development along with image development. In order to obtain satisfactory photographic quality it is necessary to restrain the fog, preferably with as little effect as possible on the effective emulsion speed and contrast.

When evaporated silver halide films are placed in a developer, surface-abrasion marks have more tendency to develop than is the case when conventional films are so treated. Both the fogging propensity and the sensitivity to mechanical abrasion appear to be related to the absence of gelatin or other Vehicle for the silver halide. Polymericresin vehicles, such as gelatin, physically isolate and protect the silver halide and presumably contribute to the cleaner development of conventional silver halide emulsions compared to that of evaporated silver halide layers of comparable speed, contrast, and graininess properties.

Normal antifoggants do not satisfactorily control this fog, and there is a need for an improved developing procedure which will produce clean working developments at good speed, contrast and acutance levels.

We have found that such an advantageous result can be achieved by developing in the presence of a synergistic combination of two well-known classes of silver halide reactants.

It is an object of our invention to provide synergistic combinations of reagents which promote clean-Working development of binderless silver halide films at excellent speed, contrast and acutance levels.

It is another object to provide such combinations of 3,335,009 Patented Aug. 8, 1967 reagents which can be incorporated in the developing solution, in a pre-bath, or in an overlayer on an evaporated silver halide film to reduce the fog obtained in the 0 development of such materials without adversely affecting speed.

It is a further object to provide combinations of two addenda which show outstanding synergism in overcoming development fog and abrasion fog in the processing of evaporated silver halide films, and which co-act in concentrations low enough to minimize the adverse effects characteristic of the separate agents when either is used in sufficiently high concentration alone to substantially decrease fog.

Still another object of this invention is to provide novel, binderless silver halide photographic elements which have reduced tendency to fog during development.

We have achieved these and other objects which will become apparent in the following description of our invention, by developing binderless, silver halide photosensitive layers in the presence of a mixture comprising two silver halide reactants, one of which forms a highly water-insoluble silver complex, the other of which forms a highly water soluble silver-salt complex. We have found that the photographic prints obtained in accordance with this invention have substantially less fogthan when similar exposed photographic elements are developed by prior art processes.

Our invention encompasses development of binderless silver halide layers in the presence of a combination of (l) a heterocyclic mercaptan which forms a silver salt of low water solubility and (2) a complexing agent which reacts with silver halide to form a highly water-soluble complex.

The heterocyclic mercaptans useful in our invention include compounds of the types commonly used in conventional photographic silver halide processes as image stabilizers, blue black toning, anti-plumming, and antibronzing agents, toning agents for physical development, antifoggants, emulsion stabilizers, and the like.

These agents preferably are employed in the developing solution. Some of them decrease fog when used alone (that is without the second component of the synergistic combination of the invention) in the development of evaporated silver halide materials, but the quantities required to restrain f-og also cause severe loss in speed, reduction in contrast, and general deterioration in the photographic quality.

The other member of our fog-reducing combination is selected from the class of compounds which react with silver chloride, silver bromide, and silver iodide to form highly water-soluble complexes. This property has resulted in their use as fixing agents for stabilizing developed silver halide materials; as carriers for the silver ion in silver-salt diffusion transfer systems; as solubilizing agents, and metal-ion-buffering agents in intensifying solutions, which depend on the electroless deposition of metal ions in the presence of a reducing agent onto particulate matter, such as a metal image, e.g., a silver photographic image.

The heterocyclic mercaptans employed in the practice of this invention are heterocyclic nitrogen compounds cont-aining at least one mercapto function which is bonded to a carbon atom which is in the alpha position with respect to a nitrogen atom in a heterocyclic ring. The heterocyclic nucleus of such compounds contains one or more heterocyclic rings wherein the heterocyclic atoms (i.e., atoms other than carbons, including nitrogen, oxygen and sulfur) are members of at least one heterocyclic ring which can be fused or condensed to one or more rings which do not contain heterocyclic atoms. In contrast, diheterocyclic nitrogen compounds contain fused or condensed heterocyclic rings in which the heterocyclic atoms are members of two heterocyclic rings. Suitable heterocyclic nitrogen compounds from which the heterocyclic nuclei can be derived include the azoles, (e.g., benzothiazoles), oxazoles (e.g., benzoxazoles), diazoles (e.g., imidazoles, benzimidazoles, imidazolines, oxadiazoles, thiadiazoles), triazoles (e.g., 1,2,4-triazoles), pyrimidines, 1,2,4-triazines, s-triazines, tetrazoles, urazoles, oxazolines, thiadiazines, azaindenes (e.g., tetrazaindenes) and the like.

Mercapto heterocyclic nitrogen compounds which can be employed in the practice of this invention can be represented by the formula:

where Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from to 6, preferably 5, atoms in a heterocyclic ring and SX is a mercapto function. The mercapto function or group can be in the free (SH) form or in the salt (SX) form.

r X is a cation, for example, hydrogen, an alkali metal such as sodium or potassium, ammonium or an organic amine residue of such amines as triethyl amine, triethanol amine, morpholine and the like. In addition, many of the mercaptoheterocyclic nitrogen compounds can be in the tautomeric form, for example, in the thione form, in which case the labile hydrogen atom in the mercapto function becomes bonded to the nitrogen atom and the group becomes a thiocarbonyl C S) group.

Any of the heterocyclic compounds which contain at least one nitrogen atom and a mercapto function, as described heerin may be used in the practice of this invention. However, particularly good results are obtained with the mercaptoazoles, especially the S-mercaptotetrazoles. 5-mercaptotetrazoles which can be employed in the practice of this invention include those having the formula:

3-mercapto-1,2,4-triazole Z-mercapto-S-phenyl-1,3,4-oxadiazole 1-methyl-2-mercaptoimidazole Z-mercaptobenzimidazole 2-mercaptobenzoxazole 5-methyloxazoline-Z-thiol S-mercapto-1phenyl-1,2,3,4-tetrazole (8) 4-phenyliminothiourazole (9) 2-mercaptothiazoline 10) Z-mercapto-S-methyl-1,3,4-thiadiazine (11) 2-amino-5 -mercapto-1,3,4-thiadiazole 12) 2-mercaptobenzothiazole 13) 2,6-dimethyl- 1 ,3,3 a,7 -tetrazaindene-4-thiol (14) 4-hydroxy-6-methyl- 1,2,3 a,7-tetrazaindenc-3 -thiol A number of such suitable mercaptohetreocyclic nitrogen compounds are disclosed in Tregillus et al. US. Patent 3,017,270, issued Jan. 16, 1962.

The second component of the mixture of complexing agents useful in our invention is a highly water-soluble reactant which complexes with silver ions. Some specific examples of complexing agents which can be employed in the practice of our invention are, for example, (1) alkali metal and ammonium thiosulfates, (2) alkali metal and ammonium thiocyanates, (3) a mixture of potassium bromide and sodium sulfite, (4) 2-aminoethanol, (5) sulfur dioxide addition products of Z-aminoethanol, prepared by adding gaseous sulfur dioxide to 2-amino ethanol, (6) di(2-hydroxy) ethyl amine, (7) a monoaliphatic amine having from 6 to 10 carbon atoms, such as 1-aminohexane, (8) monoalicyclic amines wherein the alicyclic ring containing 6 carbon atoms, such as cyclohexylamine and its methyl and ethyl derivatives, and (9) amine thiosulfate 'anhydrides, e.g., 2-amino ethanol thiosulfate anhydride as disclosed in US. Patent No. 3,169,992. Best results are obtained with the thiosulfate and thiocyan ate salts or 2- amino ethanol.

An alternative method of reducing fog is to use a developer prepared by dissolving a divalent vanadium salt in an anhydrous alcohol or a mixture of anhydrous alcohol and an anhydrous ether, e.g., an equal volume mixture of ethyl alcohol and diethyl ether. This developer is most elfective in the temperature range of to -60 C. using development times of from three to fifteen minutes.

The mercaptoheterocycle may be incorporated in a water-permeable colloid overcoat on the vapor-deposited silver halide layer, and the silver halide solvent may be incorporated in the developing composition, or they may both be incorporated in the developing solution. To obtain the beneficial synergism which characterizes our invention it is essential only that development take place in the presence of both constituents.

Developer solutions useful in the practice of our invention can be prepared by adding the fog-reducing combination of a heterocyclic mercaptan and a silver halide complexing agent to a developing composition comprising developing agents, such as aminophenols, e.g., p-methylaminophenol sulfate, hydroquinones, and 3-pyrozolidones, such as 1-phenyl-3-pyrazolidone, and other addenda such as sodium sulfite, alkaline buffer and the like.

The fog reducing agents and silver halide complexing agent are used in combination in concentrations effective to reduce fog without adversely affecting the photographic properties of the element. Preferably, the synergistic combinations of compounds are added to the developer. However, if desired, the fog reducing agent may be incorporated in a hydrophilic coating over the binderless silver halide layer, and just the silver halide complexing agents added to the developer. In another arrangement, the synergistic combination of compounds of this invention are incorporated in a hydrophilic coating applied over the binderless silver halide layer, but separated from the silver halide layer by a suitable barrier layer, such as gelatin. When the silver halide complexing agent is employed in an overcoating, it is desirable to employ a barrier coating between the silver halide and the layer containing the complexing agent to prevent the complexing agent from adversely affecting the photographic properties of the element.

The heterocyclic mercaptans are especially effective in the range of from about 0.01 to about 0.4 gram per liter of developer solution. Preferably, these compounds are employed at a concentration of about 0.05 gram to about 0.1 gram per liter of developer. The silver halide complexing agents are most useful in the range of about 1 gram to about 10 grams per liter of developer solution, and are preferably employed at from about 3 to 6 grams per liter of developer solution.

When an attempt is made to control fog by the use of heterocyclic mercaptans alone or silver halide complexing agents alone much higher concentrations are required to overcome development fog and abrasion fog in the processing of evaporated silver halide films, and the effective speed, contrast, and maximum density of the photographic image are drastically lowered. Accordingly it was highly surprising to find that the adverse effects characteristic of these agents when used separately are obviated and photographic images of good quality and low fog density are obtained when development is carried out in the presence of a combination of appropriate concentrations of these materials.

The evaporated silver halide films used in our invention may be coated on a variety of supports, such as paper, film, plastic or glass. The fog-reducing characteristics of our combination of addenda are not affected by the thickness of the silver halide layer. Substantial fog reduction has been achieved with layers varying in thickness from about 100 m to about 550-1'1'1,u.

In the practice of our invention, vacuum-deposited silver halide layers are exposed to a light pattern, processed in the presence of our fog-reducing combination by immersion in a developer solution or by surface application of such a solution.

The following examples illustrate the mode of operation of our invention as well as its novel and unexpected aspects.

Example 1 Grams Elon 3 Sodium sulfite, desiccated 45 Hydroquinone 12 Sodium carbonate, monohydrated 80 Potassium bromide 2 Water to make 1 liter.

which is marketed as Kodak Developer D72, said developer being modified as follows:

Sample Addenda Relative Fog Speed 1 (control) 100 0. 2 4 gjliter of sodium thiosulfate 160 0. 3 0.3 gJliter of 5-mercapto-l-phenyl 70 O.

tetrazole. 4 .1 4 g./liter of sodium thiosulfate and 160 0.00

' 0.1 g./liter oi 5-mercapto-1-phenyltetrazole.

It is seen that fogging was reduced by the addition of sodium thiosul-fate to the developer, and subsequently eliminated by the synergistic action of the heterocyclic mercaptan and the silver halide complexing agent. The use of the heterocyclic mercaptan alone while reducing fog also causes a severe loss in speed.

Example 2 Similar results were obtained when the procedure of Example 1 was repeated with 0.2 g. per liter of 3-mercapto-1,2,4-triazole as the heterocyclic mercaptan and 4 g. of sodium thiocyanate as the silver halide complexing agent.

New

Example 3 A coating was prepared as described in Example 1, except that a layer of silver bromide 500 m thick was deposited. A sample of the film was exposed behind a. step wedge and developed for 12 seconds at 72 F. in the following solution:

1-phenyl-3-pyrazolidone grams 0.5 Ascorbic acid do 10.0 Z-methylaminoethanol ml 31.0 Potassium bromide grams 10.0

Water to 1.0 liter.

The pH was adjusted to 10.4 with sodium hydroxide.

The image was formed having a high, uneven fog density of 0.4 to 0.8. When a sample of film was developed under the same conditions in a solution of the above formula to which was added 4 grams per liter of potassium thiocyanate and 0.4 gram per liter of 4-phenyliminothiourazole an image with even fog density of 0.04 was formed.

An alternative procedure for obtaining selective development in exposed vapor-deposited silver halide layers is provided, as shown below, by ultra-low temperature development with an inorganic reducing agent such as a divalent vanadium salt dissolved in a non-aqueous organic medium, such as ethanol or n-butanol or a combination of ethanol and an ether such as diethyl ether.

Example 4 A light-sensitive layer of silver bromide vapor deposited on clay-coated paper as in Example 1 is cut into 6 strips which are developed as follows:

Strip Developer Develop- Fog ing time 1 (control).. Kodak D72 at 20 C 14 sec 0.2-0.4- 2 Kodak D72 modified as in Sample 14 sec 0.0

3 of Example 1 at 20 C.

3 Vgiapdcium dichloride developer at O. 5 sec 1.2 As strip 3 at 0 0 5 sec 0.4-0.6

As strip 3 at -60 C 3 min 0. 0

As strip 3 at -90 C 15 min 0.0

The vanadium dichloride developer was prepared in the following manner. Vanadium trichloride was dissolved in anhydrous ethyl alcohol at a concentration of 125.6 grams per liter. This solution was acidified slightly with hydrogen chloride gas. The solution was then allowed to flow through a column of amalgamated zinc at a rate sufficient to reduce 90 percent of the trivalent vanadium to the divalent state. The solution was chilled immediately to C. and diluted with an equal portion of diethyl ether which was chilled to 80 C.

The developed strips are fixed in a conventional fixing bath, washed and dried. As shown in the above table, strips are developed at successively lower temperatures. It is found necessary to go below 0 C. in order to reduce fog to a satisfactory, low level. Strip No. 3 developed non-selectively while Strip No. 6 was fog-free and comparable in other sensitometric properties to Strip No. 2.

Example 5 The synergistic effect of combinations of small amounts of certain heterocyclic mercaptans and silver halide complexing agents is demonstrated further by the following series of examples.

A silver bromide coating was prepared by vapor deposition on a baryta coated, photographic paper stock as described in Example 1. Several samples of this paper were 7 sensitometrically exposed and processed in several developers with the following results:

Density- Developer Chemical Relative Dmnx plus Abra- Speed sion Fog Kodak D-72 developer, modified,

containing:

(1) No addenda (control) 0.2 100 1.2 (2) 0.1 gram per liter S-niethyl oxazoline-Z-thiol .t 0. H). 2 100 1. 2 (3) 0.2 gram per liter 5-Inethyl oxazoline-2-thiol None 50 0.7 (4) 4 grams per liter sodium thiosultate .5 H O 0.1-0.2 140 1. 2 (5) 8 grams per liter sod In thiosulfate .5 Hi None 63 0.9 6) 4 grams per liter sodium thiosulfate .5 H 0, plus 0.1 gram per liter -methyloxazoline-2-thiol None 100 1.2

All samples were given full development, and when fog was obtained, it was uneven and grainy.

It is seen that when either the silver halide solvent or the heterocyclic mercaptan is used in sufficient concentration to eliminate fog, the sensitometric properties of the material are adversely aifected, as is shown by Tests 3 and 5. However, the proper combination of these agents as in Test 6 will control fog without causing losses in speed, contrast and maximum density. Combinations of other silver halide solvents with heterocyclic mercaptans are also elfe-ctive as shown by the following results:

Density- Developer Chemical Relative D ux plus Abra- Speed sion Fog Kodak D-72 developer, modified containing:

(1) N0 addenda (control) 0.2 100 1.2 (2) 15 grams per liter sodium thiocyanate 0.01-0. 100 0.7 (3) 0.4 gram per liter 5-mercaptol-phenyl l,2,3,4-tetrazole 0.01-0. 10 83 1.0 (4) 0.4 gram per liter fi-mercapto- 1 phenyl 1,2,3 .4-tetrazole plus 9 grams per liter sodium thiocyanate None 100 1.2 (5) 2.5 grams per liter Z-aminoethanol 0. 5 100 1. 2 (6) 2.5 grams per liter 2-aminoethanol plus 0.2 gram per liter 5-mercapto-1-phenyl-1,2,3,4-tetrazole 0.01-0.02v 100 1.2

Example 6 A photographic element is prepared as described'in Example 1 except that the silver halide is overcoated with a gelatin layer containing S-mercapto-l-phenyl tetrazole. This element is exposed and developed for 14 seconds at 72 F. in Kodak Developer D-72 to which is added 4 grams per liter of sodium thiosulfate. The results obtained are similar to those obtained in Sample 4 of Example 1.

Example 7 A photographic element is prepared as in Example 1, and the silver halide is overcoated with a barrier layer of gelatin, and the barrier layer is in turn overcoated with a gelatin layer containing sodium thiosulfate and S-mercapto-l-phenyl tetrazole. This element is exposed and developed for 14 seconds at 72 F. in Kodak Developer D-72. The results obtained are similar to those in Sample 4 of Example 1.

Although the invention has been described in considerable detail with particular reference to certain preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove, and as defined in the appended claims.

We claim:

1. The process for providing photographic images in an exposed, binderless silver halide photographic layer which comprises developing said layer in the presence of a heterocyclic nitrogen compound having the formula:

where Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from 5 to 6 atoms in a heterocyclic ring and SX represents a mercapto group, and a complexing agent selected from the group consisting of the alkali metal thiosulfates, ammonium thiosulfate, alkali metal thiocyanates ammonium t-hiocyanate and Z-amino ethanol, said compound and complexing agent being present in a concentration sufiicient to effectively reduce fog without substantially reducing the speed of the photographic layer.

2. The process for providing photographic images in an exposed, binderless silver halide photographic layer which comprises developing said layer in the presence of a mercapto-tetrazole compound, and a complexing agent selected from the group consisting of the alkali metal thiosulfates, ammonium thiosulfate, alkali metal thiocyanates, ammonium thiocyanate and Z-aminoethanol, said mercapto terazole and complexing agent being present in a concentration sufiicient to effectively reduce fog without substantially reducing the speed of the photographic layer.

3. A process for providing photographic images in an exposed binderless silver halide photographic layer which comprises contacting said layer with a developer containing from about 0.01 to about 0.04 gram of a mercapto tetrazole per liter of developer solution, and from about 1 to 10 grams, per liter of developer solution of a complexing agent selected from the group consisting of the alkali metal thiosulfates, ammonium thiosulfate, the alkali metal thiocyanates, ammonium thiocyanate and Z-aminoethanol.

4. A process for providing photographic images in an exposed, vapor-deposited silver halide layer which comprises contacting said layer with a developer containing:

Grams Elon 3 Sodium sulfite, desiccated 45 Hydroquinone 12 Sodium carbonate, monohydrated Potassium bromide 2 Water to make 1 liter.

to which has been added approximately 4 grams per liter of sodium thiosulfate and approximately 0.1 grams per liter S-mercapto-l-phenyltetrazole.

5. A photographic element comprising a support having coated thereon a binderless, light sensitive silver halide layer overcoated with a hydrophilic colloid coating containing a compound having the formula colloid containing (1) a compound having the formula where Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing from to 6 atoms in a heterocyclic ring and SX represents a mercapto group, and (2) another compound selected from the group consisting of the alkali metal thiosulfates, ammonium thiosulfate, alkali thiocyanates, ammonium thiocyanate and 2-amino ethanol, said compounds being present in a concentration :sufficient to effectively reduce fog during development of said layer Without substantially reducing the speed of the photographic layer.

8. A photographic element comprising a support having coated thereon, in the following order, a binderless light sensitive silver halide layer, a hydrophilic colloid barrier layer and an overcoating comprising a hydrophilic colloid containing (1) a mercapto tetrazole and (2) a complexing agent selected from the group consisting of the alkali metal thiosulfates, ammonium thiosulfate, the alkali metal thiocyanates, ammonium thiocyanate and Z-aminoethanol said mercapto tetrazole and complexing agent being present in a concentration suflicient to eifectively reduce fog during development of said layer with- 10 out substantially reducing the speed of the photographic layer.

References Cited UNITED STATES PATENTS 7/1946 Kendall et a1. 9666 1/1958 Goldschein 9676 OTHER REFERENCES Cook, F. H., et al.; Amisotropic Photographic and Related Properties of Monocrystalline Silver Chloride, AF Technical Report No. 54-486, AD No. 61943, Virginia Institute for Scientific Research, March 1955, pp. 10, 11.

Goldberg, G. M., et al.; Investigations on Extending the Sensitivity Range of Silver Crystals and Evaporated Films of Silver Bromide, Technical Operations, Inc., Report No. TO-B-6137, Contact No. AF 33(616)-6992, August 1961, p. 48, AD No. 264061.

Technical Documentary Report No. ASDTDR-63 598, AD 412,775, Research on High Acuity Continuous Tone Vacuum Evaporated Silver Bromide Films, May 1963, AP Avionics Laboratory, Project No. 6272, Task No. 627209, ASTIA, Arlington, Va., pp. 39-46.

NORMAN G. TORCHIN, Primary Examiner.

C. E. DAVIS, Assistant Examiner. 

1. THE PROCESS FOR PROVIDING PHOTOGRAPHIC IMAGES IN AN EXPOSED, BINDERLESS SILVER HALIDE PHOTOGRAPHIC LAYER WHICH COMPRISES DEVELOPING SAID LAYER IN THE PRESENCE OF A HETEROCYCLIC NITROGEN COMPOUND HAVING THE FORMULA: 